The present invention is directed to a method for the preparation of a fluorosulfonyl imide monomer useful for forming ionomers. Such ionomers are useful in electrochemical applications such as batteries, fuel cells, electrolysis cells, ion exchange membranes, sensors, electrochemical capacitors, strong acid catalysts, and modified electrodes.
Monomers represented by the formula
CF2=CFOCF2CF2SO2Fxe2x80x83xe2x80x83(I)
are employed by Ezzell et al., U.S. Pat. No. 4,940,525 to form copolymers with TFE followed by hydrolysis to the ionomer form. Ionomers of the type disclosed by Ezzell are suitable for a variety of electrochemical applications including the chloralkali process.
Putnam et al., U.S. Pat. No. 3,301,893, or in the alternative Resnick, U.S. Pat. No. 3,560,568, discloses a process for preparing CF2=CFOCF2CF2SO2F by pyrolysis of FSO2CF2CF2OCFCF3COONa. Resnick, op.cit., forms a cyclic sulfone of the formula 
by pyrolyzing the FSO2CF2CF2OCFCF3C(O)F of Putnam in the presence of Na2CO3. Resnick then reacts the cyclic sulfone (II) with sodium methoxide to form CF2=CFOCF2CF2SO3Na which is then converted through a series of steps to the monomer (I) followed by copolymerization with TFE and subsequent hydrolysis to the ionomer form.
Putnam discloses the generalized reaction scheme 
where X is CF3- or F, and Rf is F or perfluoroalkyl.
Xue, Ph.D. Thesis, Clemson University, 1996, shows that a composition containing CF3SO2NNa2 when reacted with the cyclic sulfone (II), provides a 4% yield of CF2=CFOCF2CF2SO2N(Na)SO2CF3 (III) amidst a much larger yield of saturated species. Xue provides no method for achieving a higher yield of (III). There is no teaching in Xue in regard to the concentration of CF3SO2NNa2 in the reaction mixture, nor as to the relationship between yield of (III) and the concentration of the CF3SO2NNa2.
DesMarteau, U.S. Pat. No. 5,463,005, discloses the copolymer of (III) with tetrafluoroethylene to form an ionomer. Feiring et al., WO9945048(A1), disclose the copolymer of (III) with vinylidene fluoride to form a lithium ionomer.
The present invention is a process for forming, at a yield greater than 50 mol-%, a monomeric composition represented by the formula
(CF2=CFOCF2CFXSO2N(M)SO2Ryxe2x80x83xe2x80x83(IV)
wherein X is F or perfluoroalkyl having 1-4 carbons optionally substituted by ether oxygen, M is an alkali or alkaline earth metal when y is respectively 1 or 2, R is aryl, fluoro-aryl, or XCF2- where X is H, halogen, fluorinated or non-fluorinated linear alkyl having 1-10 carbons or cyclic alkyl having 3-10 carbons, optionally substituted by one or more ether oxygens;
the process comprising:
contacting in an inert atmosphere a cyclic sulfone represented by the structure 
wherein X is F or perfluoroalkyl having 1-4 carbons optionally substituted by ether oxygen with a composition sulfonyl amide salts of which said salts at least 50 mol-% are sulfonyl amide salts represented by the formula
(RSO2NMb)3-bMxe2x80x2cxe2x80x83xe2x80x83(V)
wherein R is aryl, fluoro-aryl, or XCF2- where X is H, halogen, fluorinated or non-fluorinated linear alkyl radicals having 1-10
where R is aryl, fluoro-aryl, or XCF2- where X is H, halogen, fluorinated or non-fluorinated linear alkyl radicals having 1-10 carbons or cyclic alkyl radicals having 3-10 carbons, optionally substituted by one or more ether oxygens, Mxe2x80x2 is an alkaline earth metal, b=1 or 2, c=0 or 1, M is alkaline earth or alkali metal when b is 1 or 2 respectively and c=0, and M is alkali metal when b=1 and c=1, with the proviso that cxe2x89xa01 when b=2, thereby forming a ring-opening reaction mixture; reacting said ring-opening reaction mixture at a temperature in the range of 0 to 67xc2x0 C.
As used herein, the term xe2x80x9creactingxe2x80x9d is intended to mean allowing at least two components in a reaction mixture to react to form at least one product. xe2x80x9cReactingxe2x80x9d may optionally include stirring and/or heating or cooling.